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NAME
Object::Pad::FieldAttr::Isa - apply class type constraints to
Object::Pad fields
SYNOPSIS
use Object::Pad;
use Object::Pad::FieldAttr::Isa;
class ListNode {
field $next :param :reader :writer :Isa(ListNode) = undef;
}
my $first = ListNode->new();
my $second = ListNode->new(next => $first);
# This will fail
my $third = ListNode->new(next => "something else");
# This will fail
$second->set_next("another thing");
DESCRIPTION
This module provides a third-party field attribute for
Object::Pad-based classes, which declares that values assigned to the
field must conform to a given object type.
WARNING The ability for Object::Pad to take third-party field
attributes is still new and highly experimental, and subject to much
API change in future. As a result, this module should be considered
equally experimental.
FIELD ATTRIBUTES
:Isa
field $name :Isa(CLASSNAME) ...;
Declares that any value assigned to the field must be an object
reference, and must be derived from the named class. Attempts to assign
a non-conforming value, such as a non-reference, or reference to a
class not derived from that named, will throw an exception, and the
field value will not be modified.
This type constraint is applied whenever the field itself is assigned
to, whether that is from :param initialisation, invoking a :writer or
:mutator accessor, or direct assignment into the field variable by
method code within the class.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
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